The present invention relates to a mold for manufacturing polyurethane parts using the reaction injection molding process. The mold comprises two mold halves which between them enclose a mold cavity which is sealed off from the outside by a sealing surface.
When manufacturing polyurethane parts using the RIM process, spew in the parting planes of the mold halves causes considerable problems. The liquid reaction mixture, as it is poured into the mold and especially as it reacts and due to the rise in pressure, penetrates into minute gaps in the parting planes. Although advanced machine tool technology has made it possible to achieve degrees of dimensional accuracy for the contoured parting plane shapes in steel tools of a maximum gap accuracy of around 50 .mu., the reaction mixture is still able to penetrate these small gaps. The result is an extremely thin spew which is known in the industry as "flit". It is very brittle, generally breaks off from the molded part and is left as splinters in the mold.
Removal of the splinters from the mold is very laborious and is usually carried out with compressed air, causing environmental pollution. If splinters are left in the mold cavity, defects occur in the next molded part. The whole cycle is substantially prolonged by the necessity of carrying out cleaning.
The object of the present invention was the development of a mold for manufacturing polyurethane parts using the RIM process, whereby flit formation and the source of errors associated therewith could be avoided.